A fuel cell system is a system in which: a hydrogen-containing gas and an oxygen-containing gas are supplied to a fuel cell that is a main body of a power generating portion; an electrochemical reaction between hydrogen and oxygen proceeds; and chemical energy generated by this reaction is taken out as electric energy. Since the fuel cell system can perform the highly efficient electric power generation, and heat energy generated during the electric power generating operation can be easily utilized, the fuel cell system has been developed and commercialized as a distributed power generation system capable of realizing high energy use efficiency.
Since a hydrogen-containing gas infrastructure has not been developed in many cases, the fuel cell system is provided with a hydrogen generator including a reformer configured to generate a hydrogen-containing gas. At the time of start-up, the reformer is heated by a combustor, such as a burner, by using a city gas, a LPG, or the like, supplied from an existing infrastructure, as combustion fuel. With this, the hydrogen-containing gas is generated by reforming a raw material, such as the city gas or the LPG, by using a Ru catalyst or Ni catalyst of the reformer at a temperature (for example, about 600° C. to 700° C.) appropriate for a reforming reaction. After the start-up, the combustor continues the combustion by using a part of the city gas, the LPG, or the like or an unreacted hydrogen-containing gas (so-called off gas) discharged from the fuel cell.
In the hydrogen generator configured to perform the reforming reaction by using, as a material gas, the city gas, the LPG, or the like, supplied from the existing infrastructure, the combustor needs to be stably ignited at the time of the start-up and also needs to stably continue a flame holding state after the ignition.
Generally used for the ignition of the combustor at the time of the start-up is a method of diffusing a predetermined amount of material gas and combustion air in the combustor and generating sparks by an ignitor or the like provided at the combustor.
However, the specific gravity of propane is about 2.76 times the specific gravity of the city gas, and the specific gravity of the butane is 3.63 times the specific gravity of the city gas. Therefore, in a case where the mass flow rate is the same, the flow velocity of the propane is 0.36 time the flow velocity of the city gas, and the flow velocity of the butane is 0.28 time the flow velocity of the city gas. To be specific, in the case of using the propane and the butane as the combustion fuel of the combustor, because of the low flow velocities of the propane and the butane, the combustion fuel hardly diffuses in the combustor, and the stable ignition of the combustor by the mixing of the combustion air and an appropriate amount of combustion fuel becomes difficult in some cases.
Here, PTL 1 proposes a method of, when the combustor hardly ignites, facilitating the ignition of the combustor by increasing the amount of material gas supplied to the combustor to increase the concentration of the material gas supplied to the combustor.